Upon detection of a specific protein in a food, the recovery rate in the additive test and dilution linearity are not guaranteed because of strong effects of food matrix ingredients other than a target proteins contained in the food, so that appropriate detection may be difficult. Particularly when a target is a muscle protein and animal proteins are further contained as matrices in the food, the target protein and the animal proteins may form complexes. Difficulty of the appropriate detection of a target is pronounced in these cases.
In recent years, health harm cases due to foods containing allergic substances (hereinafter, referred to as allergens) have been increasingly common. A questionnaire in a research report produced by a Committee on Measures against Food Allergy has revealed that 12.6% of nursery school toddlers, 8.6% of 3-year-old children, 7.4% of first-graders, 6.3% of junior high-school students, and 9.3% of adults have some of allergic symptom. In response to the results, since April 2001 (and effective starting in April 2002) the Ministry of Health, Labour and Welfare has enforced labeling system for five specific raw materials (eggs, milk, buckwheat noodles, wheat, and peanuts, which are specific raw materials with high number of patients and high severity) used for processed foods in order to provide information about these food materials to the allergic patients and to avoid health hazards. At the same time, notification has been given regarding detection methods for the purpose of realizing appropriate labeling.
In these methods for detecting allergens, surfactants and reducing agents are used to extract allergens as measurement targets efficiently from processed foods (see Patent Document 1 and Non-Patent Documents 1 and 2). However, these protein denaturants are also involved in the formation of complexes as described above, making appropriate measurement difficult.
It has been difficult to measure target specific proteins accurately and precisely in processed foods containing various food matrices as described above.    Patent Document 1: JP Patent No. 3600231    Non-Patent Document 1: Watanabe Y. et al.: Journal of Immunological Methods 300 (2005) 115-123    Non-Patent Document 2: Dept. of Food Safety, Pharmaceutical and Food Safety Bureau, Ministry of Health, Labour and Welfare, Notice (Shokuhatsu) No. 1106001 (Attachment 1, Nov. 6, 2002 (Final revision: Jun. 22, 2006); Notice (notification given by the Department of Food Safety) No. 0622003